Editor,

Cardiac tachyarrhythmias have been treated by catheter ablation for nearly half a century.

Due to the duration and discomfort of the procedure, ablations are usually carried out either under general anaesthesia or conscious sedation. Although patient comfort is the most important immediate priority, the choice of general anaesthesia over sedation is often influenced by the type of ablation being performed.

Herein, we seek to provide a succinct overview of the practical considerations of different anaesthetic strategies for the various types of ablation procedure.

Atrial fibrillation

Atrial fibrillation, caused by chaotic electrical activity in the atria (Fig. 1), is the most common arrhythmia with a UK prevalence of 3.29%.1 Pulmonary vein isolation (PVI) using radiofrequency or cryoballoon ablation is a well established treatment for atrial fibrillation. Three-dimensional electro-anatomical mapping is often used for radiofrequency ablation, with which a left atrial ‘geometry’ is created by the movement of a mapping catheter within the chamber onto which electrical data can be superimposed to diagnose arrhythmia mechanisms and localise arrhythmogenic foci (Fig. 2). Movement during acquisition of the geometry can lead to dislocation of catheter projection relative to the anatomical map, resulting in ablation at incorrect sites, and a higher likelihood of mechanical complications due to catheter trauma.

Fig. 1:

Diagrammatic representation of chaotic disordered atrial electrical activity as the mechanism for atrial fibrillation.

Fig. 2:

Electro-anatomical maps of the left atrium created using Carto (above) and Rhythmia (below).

A popular method of delivering general anaesthesia is total intravenous anaesthesia (TIVA) using infusions of remifentanil, an ultra-short acting opioid, and propofol alongside depth of anaesthesia monitoring. Conscious sedation using opioid or benzodiazepine boluses may be used in cases where general anaesthesia is not desired.2 Use of general anaesthesia results in better contact force and a more contiguous lesion set when compared with conscious sedation for radiofrequency PVI,3 as patient immobility and controlled respiratory excursion allow better catheter stability and tissue contact.4 This translates into lower longer-term arrhythmia recurrence.3–7 Outcomes may be further improved using high-frequency jet ventilation to minimise thoracic respiratory excursion,8,9 though this is potentially offset by the added complexities associated with the technique, which limit its appeal at present. The additional time taken to anaesthetise patients appears to be compensated by shorter ablation time, resulting in a similar overall duration of the procedure between general anaesthesia and sedation.4,7

Left atrial geometry is not required for cryoballoon ablation, and accordingly, general anaesthesia use does not appear to confer any outcome advantage.10 In contrast to radiofrequency procedures, however, overall laboratory times are longer when general anaesthesia is used.

Heterogeneous strategies across studies make direct safety comparison between general anaesthesia and sedation difficult, though complication rates are low overall. Hypotension is frequently observed with general anaesthesia or deep sedation use, particularly in older patients. This is generally mild and reversible with no reports of procedure abandonment or longer-term sequelae.4,11–13 Postprocedure complications arising from general anaesthesia/deep sedation are significantly more frequent in patients at least 75 years of age.11 Thus, once out of the laboratory, an appropriate period of observation is necessary to assess for anaesthesia-related complications.14 TIVA decreases the incidence of postprocedure nausea and delirium compared with volatile anaesthetics15 and reduces the requirement for neuromuscular blockers, thereby avoiding the adverse effects associated with this.16

There is no significant difference in the rate of major complications, such as atrio-oesophageal fistula, cardiac tamponade or death, between atrial fibrillation ablation under general anaesthesia or conscious sedation. Higher rates of thermal oesophageal injury have been reported in general anaesthesia cases,17 but all lesions are normalised by 2 months.

Supraventricular tachycardia

Supraventricular tachycardia (SVT) is a term that covers atrioventricular nodal re-entrant tachycardia (AVNRT), atrioventricular re-entrant tachycardia (AVRT) and atrial tachycardia (Fig. 3). Arrhythmia induction is required during ablation to clarify the diagnosis and map the substrate. This requirement and the relatively short ablation time therefore support the use of light sedation over general anaesthesia in SVT ablation in adults.

Fig. 3:

Schematic diagram representing mechanisms of supraventricular tachycardia.

General anaesthesia can suppress arrhythmia induction through dampening of afferent sympathetic inputs on the cardiac conduction system. Furthermore, isolated case reports describe termination of SVT following propofol administration,18 which may be due to its inhibitory effect on cardiac ion channels.19,20 In addition, dexmedetomidine may depress sinus and atrioventricular node function due to sympatholytic properties.21 However, neither propofol nor dexmedetomidine use appears to affect baseline electrophysiological parameters or arrhythmia inducibility,22,23 although sympathomimetic agents such as isoprenaline or ketamine coadministration are more frequently required for tachyarrhythmia induction.24,25

Typical atrial flutter ablation does not require arrhythmia induction, as there is a clearly defined critical anatomical target for ablation, the cavotricuspid isthmus (Fig. 4). Typical flutter ablation is a shorter and generally less uncomfortable procedure than radiofrequency atrial fibrillation ablation, and conscious sedation is usually adequate.26

Fig. 4:

Diagrammatic representation of a macro re-entrant, anticlockwise circuit around the right atrium, characteristic of typical atrial flutter, with a critical isthmus for ablation: the cavotricuspid isthmus (zigzagged line).

Ventricular tachycardia

Focal ventricular tachycardia can occur due to abnormal automaticity or triggered activity most frequently in the right or left ventricular outflow tract. Ablation for outflow tract ventricular tachycardia relies on triangulating the source of premature ventricular contractions (PVCs) to a specific area of myocardium. The higher the PVC frequency, the higher is the likelihood of accurate localisation and procedural success. Comparison studies between sedation strategies for outflow tract ventricular tachycardia ablation are lacking. Accepted practice is to provide light sedation, if needed, to avoid PVC suppression.

Re-entrant ventricular tachycardias result from a circuit created by the adjacency of rapidly conducting healthy myocardium to an area of slowly conducting scar. Patients often have structurally abnormal hearts with poor contractile reserve. Ventricular tachycardia induction is dependent on the contribution of modulating factors such as autonomic tone and focal triggers. International guidelines caution against the use of general anaesthesia for ventricular tachycardia ablation where possible,27 largely due to the suppression of sympathetic tone and the direct molecular influence of some anaesthetic agents on myocardial conductivity.27,28 Nevertheless, ventricular tachycardia ablation can be a long procedure and general anaesthesia may be warranted for patient comfort and stillness.

The combination of ventricular tachycardia provocation and the hypotensive effects of general anaesthesia renders haemodynamic management challenging, with greater reliance on intravenous inotropic support compared to sedation.29 Invasive blood pressure monitoring may aid early identification and treatment of haemodynamic instability, and reliable vascular access is obligatory. A peripheral intravenous cannula will often suffice, but it is important to have resources available to secure central venous access without delay should the need arise.

Conclusion

Cardiac electrophysiology procedures are wide-ranging. Generally, minimal sedation is more desirable for re-entrant and automatic arrhythmias, as this increases the chances of successful arrhythmia induction whilst minimising intra-procedural haemodynamic disturbance. For radiofrequency atrial fibrillation ablation, wherein arrhythmia induction is not required, there is evidence suggesting that general anaesthesia use confers better long-term outcomes.

Acknowledgements relating to this article

Assistance with article: none.

Financial support and sponsorship: none.

Conflicts of interest: none.

This manuscript was handled by Mona Momeni.

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